Field of the Invention
The present invention relates to an organic light emitting diode. More particularly, the present invention relates to an organic light emitting diode that emits white light.
Discussion of the Related Art
An organic light emitting diode has a structure in which a light-emitting layer is formed between a cathode injecting electrons and an anode injecting holes. The electrons generated from the cathode and the holes generated from the anode are injected into the light-emitting layer, and the injected electrons and holes are combined to generate excitons. The generated excitons transition from an excited state to a ground state to emit light.
Such an organic light emitting diode can be variously applied to an illumination, a thin light source of a liquid crystal display apparatus, a display apparatus, and the like. Particularly, the organic light emitting diode emitting white light can be applied to a full-color display apparatus in combination with a color filter.
The organic light emitting diode emitting white light may include a light-emitting portion emitting blue light and a light-emitting portion emitting yellow-green light. In this case, the blue light and the yellow-green light emitted from the light-emitting portions are combined and white light is finally emitted.
Hereinafter, an organic light emitting diode according to the related art will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view of an organic light emitting diode according to the related art.
As can be seen from FIG. 1, the organic light emitting diode according to the related art includes a first electrode 1, a first light-emitting portion 2, a second light-emitting portion 3, a third light-emitting portion 4, and a second electrode.
The first electrode 1 may function as an anode.
The first light-emitting portion 2 is formed on the first electrode 1 and is configured to emit blue light. The first light-emitting portion 2 includes a hole transporting layer, an electron transporting layer, and a blue light-emitting layer between the hole transporting layer and the electron transporting layer.
The second light-emitting portion 3 is formed on the first light-emitting portion 2 and is configured to emit yellow-green light. The second light-emitting portion 3 includes a hole transporting layer, an electron transporting layer, and a yellow-green light-emitting layer between the hole transporting layer and the electron transporting layer.
The third light-emitting portion 4 is formed on the second light-emitting portion 3 and is configured to emit blue light. The third light-emitting portion 4 includes a hole transporting layer, an electron transporting layer, and a blue light-emitting layer between the hole transporting layer and the electron transporting layer.
The second electrode 5 is formed on the third light-emitting portion 4 and may function as a cathode.
In the organic light emitting diode according to the related art, blue light emitted from blue light-emitting layers in the first light-emitting portion 2 and the third light-emitting portion 4 and yellow-green light emitted from a yellow-green light-emitting layer in the second light-emitting portion 3 are combined and white light is emitted. In general, the emission efficiency of blue light is lower than the emission efficiency of yellow-green light. Accordingly, two light-emitting portions of the first light-emitting portion 2 and the third light-emitting portion 4 include the blue light-emitting layer.
However, the organic light emitting diode according to the related art has a problem with a color defect in which color coordinates of white light fluctuate depending on individual pixel positions and uniform white light is not emitted from the entire screen. This problem will be more specifically described below with reference to FIG. 2.
FIG. 2 is a graph illustrating color coordinate values of white light by pixel positions in the organic light emitting diode according to the related art.
In FIG. 2, the horizontal axis represents the pixel position and the vertical axis represents the color coordinate value. FIG. 2 illustrates X-axis color coordinate values and Y-axis color coordinate values of white light which are measured at a total of fifteen pixel positions from the left to the right of a screen.
As illustrated in FIG. 2, it can be seen that the X-axis color coordinate value and the Y-axis color coordinate value are not constant but fluctuate depending on the pixel positions. Particularly, at some pixel positions, for example, at the fourth and thirteenth pixel positions, the X-axis color coordinate value is almost equal to the Y-axis color coordinate value. At the third pixel position, the X-axis color coordinate value is greater than the Y-axis color coordinate value. When the X-axis color coordinate value increases in the color coordinate system in this way, the emitted white light becomes reddish. As a result, since reddish white light is emitted from only some pixel positions of the entire screen in the related art, there is a problem in that image quality is lowered.